Lithographic apparatus and device manufacturing method

ABSTRACT

A porous member is used in a liquid removal system of an immersion lithographic projection apparatus to smooth uneven flows. A pressure differential across the porous member may be maintained at below the bubble point of the porous member so that a single-phase liquid flow is obtained. Alternatively, the porous member may be used to reduce unevenness in a two-phase flow.

This application is a continuation of U.S. patent application Ser. No.15/333,044, filed Oct. 24, 2016, now allowed, which is a continuation ofU.S. patent application Ser. No. 14/806,395, filed Jul. 22, 2015, nowU.S. Pat. No. 9,507,278, which is a continuation of U.S. patentapplication Ser. No. 13/186,123, filed Jul. 19, 2011, now U.S. Pat. No.9,097,992, which is a continuation of U.S. patent application Ser. No.12/541,755, filed Aug. 14, 2009, now U.S. Pat. No. 8,446,563, which is acontinuation of U.S. patent application Ser. No. 11/212,921, filed Aug.29, 2005, now U.S. Pat. No. 7,602,470, which is a continuation-in-partof U.S. patent application Ser. No. 10/921,348, filed Aug. 19, 2004, nowU.S. Pat. No. 7,701,550. The entire content of each of the foregoingapplications is hereby incorporated by reference.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective numerical aperture (NA) of thesystem and also increasing the depth of focus.) Other immersion liquidshave been proposed, including water with solid particles (e.g. quartz)suspended therein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, United States patent U.S. Pat. No.4,509,852, hereby incorporated in its entirety by reference) means thatthere is a large body of liquid that must be accelerated during ascanning exposure. This requires additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate (the substrategenerally has a larger surface area than the final element of theprojection system). One way which has been proposed to arrange for thisis disclosed in PCT patent application no, WO 99/49504, herebyincorporated in its entirety by reference. As illustrated in FIGS. 2 and3, liquid is supplied by at least one inlet IN onto the substrate,preferably along the direction of movement of the substrate relative tothe final element, and is removed by at least one outlet OUT afterhaving passed under the projection system. That is, as the substrate isscanned beneath the element in a −X direction, liquid is supplied at the+X side of the element and taken up at the −X side. FIG. 2 shows thearrangement schematically in which liquid is supplied via inlet IN andis taken up on the other side of the element by outlet OUT which isconnected to a low pressure source. In the illustration of FIG. 2 theliquid is supplied along the direction of movement of the substraterelative to the final element, though this does not need to be the case.Various orientations and numbers of in- and out-lets positioned aroundthe final element are possible, one example is illustrated in FIG. 3 inwhich four sets of an inlet with an outlet on either side are providedin a regular pattern around the final element.

SUMMARY

In the immersion lithography arrangements described herein, removal ofan immersion liquid typically involves a two-phase flow—the immersionliquid mixes with ambient gas (e.g., air) or gas from a gas seal used toconfine the immersion liquid. Such a two-phase flow is not very stable,especially when large pressure differentials are used to create stronggas flows to confine the immersion liquid or to ensure that all liquidis collected, and the resulting vibration is undesirable. High pressuregas flows may also cause evaporative drying of liquid remaining on thesubstrate leading to thermal gradients. Gas flows spilling over into thepath of interferometer beams may also affect the accuracy of substratetable position measurements because the interferometer is very sensitiveto changes in the refractive index of the gas in the path of theinterferometer beams, such as may be caused by changes in temperature,pressure and humidity.

Accordingly, it would be advantageous, for example, to provide anarrangement to remove liquid from the vicinity of the substrateeffectively and without generating significant vibration or otherdisturbances.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate using a projection system and havinga liquid supply system arranged to supply a liquid to a space betweenthe projection system and the substrate, comprising a liquid removalsystem including:

a conduit having an open end adjacent a volume in which liquid may bepresent;

a porous member between the end of the conduit and the volume; and

a suction device arranged to create a pressure differential across theporous member.

According to an aspect of the invention, there is provided a devicemanufacturing method, comprising:

projecting a patterned beam of radiation through a liquid onto asubstrate using a projection system; and

removing liquid from a volume by providing a pressure differentialacross a porous member bounding at least in part the volume.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 depicts a liquid removal device according to a particularembodiment of the invention;

FIG. 7 is an enlarged view of part of FIG. 6;

FIG. 8 depicts a liquid supply and removal system according to aparticular embodiment of the invention;

FIG. 8a depicts a variant of the liquid supply and removal system ofFIG. 8;

FIG. 9 depicts a variant of the liquid supply and removal system of FIG.8;

FIG. 10 depicts another variant of the liquid supply and removal systemof FIG. 8;

FIG. 11 depicts still another variant of the liquid supply and removalsystem of FIG. 8;

FIG. 12 depicts a liquid supply and removal system according to anotherparticular embodiment of the invention;

FIG. 13 depicts a variant of the liquid supply and removal system ofFIG. 12;

FIG. 14 depicts a manifold in a liquid removal system according toanother particular embodiment of the invention;

FIG. 15 depicts a variant of the manifold of FIG. 14;

FIG. 16 depicts a liquid flow regulation system usable in one or moreembodiments of the invention;

FIG. 17 depicts a variant of the liquid flow regulation system of FIG.16;

FIGS. 18 and 19 depict hydrophobic and hydrophilic capillaries used toextract liquid and gas respectively; and

FIGS. 20a to 20d depict the use of hydrophilic and hydrophobiccapillaries for separate extraction of liquid and gas from a channel.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam PB (e.g. UV radiation or DUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PLconfigured to project a pattern imparted to the radiation beam PB bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AM for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam PB is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam PB passes through the projection system PL, which focusesthe beam onto a target portion C of the substrate W. An immersion hoodIH, which is described further below, supplies immersion liquid to aspace between the final element of the projection system PL and thesubstrate W.

With the aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam PB.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe mask MA with respect to the path of the radiation beam PB, e.g.after mechanical retrieval from a mask library, or during a scan. Ingeneral, movement of the mask table MT may be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the first positioner PM. Similarly,movement of the substrate table WT may be realized using a long-strokemodule and a short-stroke module, which form part of the secondpositioner PW. In the case of a stepper (as opposed to a scanner) themask table MT may be connected to a short-stroke actuator only, or maybe fixed. Mask MA and substrate W may be aligned using mask alignmentmarks M1, M2 and substrate alignment marks P1, P2. Although thesubstrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (theseare known as scribe-lane alignment marks). Similarly, in situations inwhich more than one die is provided on the mask MA, the mask alignmentmarks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-)magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another immersion lithography solution with a localized liquid supplysystem solution which has been proposed is to provide the liquid supplysystem with a seal member which extends along at least a part of aboundary of the space between the final element of the projection systemand the substrate table. Such a solution is illustrated in FIG. 5. Theseal member is substantially stationary relative to the projectionsystem in the XY plane though there may be some relative movement in theZ direction (in the direction of the optical axis). A seal is formedbetween the seal member and the surface of the substrate.

Referring to FIG. 5, reservoir 10 forms a contactless seal to thesubstrate around the image field of the projection system so that liquidis confined to fill a space between the substrate surface and the finalelement of the projection system. The reservoir is formed by a sealmember 12 positioned below and surrounding the final element of theprojection system PL. Liquid is brought into the space below theprojection system and within the seal member 12. The seal member 12extends a little above the final element of the projection system andthe liquid level rises above the final element so that a buffer ofliquid is provided. The seal member 12 has an inner periphery that atthe upper end, in an embodiment, closely conforms to the shape of theprojection system or the final element thereof and may, e.g., be round.At the bottom, the inner periphery closely conforms to the shape of theimage field, e.g., rectangular though this need not be the case.

The liquid is confined in the reservoir by a gas seal 16 between thebottom of the seal member 12 and the surface of the substrate W. The gasseal is formed by gas, e.g., air or synthetic air but, in an embodiment,N₂ or another inert gas, provided under pressure via inlet 15 to the gapbetween seal member 12 and substrate and extracted via first outlet 14.The overpressure on the gas inlet 15, vacuum level on the first outlet14 and geometry of the gap are arranged so that there is a high-velocitygas flow inwards that confines the liquid. Such a system is disclosed inUnited States patent application no. U.S. Ser. No. 10/705,783, herebyincorporated in its entirety by reference.

FIGS. 6 and 7, the latter of which is an enlarged view of part of theformer, illustrate a liquid removal device 20 according to an embodimentof the invention. The liquid removal device 20 comprises a chamber whichis maintained at a slight underpressure p_(c) and is filled with theimmersion liquid. The lower surface of the chamber is formed of a thinplate 21 having a large number of small holes, e.g. of diameter d_(hole)in the range of 5 to 50 μm, and is maintained at a height h_(gap) in therange of 50 to 300 μm above a surface from which liquid is to beremoved, e.g. the surface of a substrate W. In an embodiment, perforatedplate 21 is at least slightly hydrophilic, i.e. having a contact angleof less than 90° to the immersion liquid, e.g. water.

The underpressure p_(c) is such that the menisci 22 formed in the holesin the perforated plate 21 prevent gas being drawn into the chamber ofthe liquid removal device. However, when the plate 21 comes into contactwith liquid on the surface W there is no meniscus to restrict flow andthe liquid can flow freely into the chamber of the liquid removaldevice. Such a device can remove most of the liquid from the surface ofa substrate W, though a thin film of liquid may remain, as shown in thedrawings.

To improve or maximize liquid removal, the perforated plate 21 should beas thin as possible and the pressure differential between the pressurein the liquid p_(gap) and the pressure in the chamber p_(c) should be ashigh as possible, whilst the pressure differential between p_(c) and thepressure in the gas in the gap p_(air) must be low enough to preventsignificant amounts of gas being drawn into the liquid removal device20. It may not always be possible to prevent gas being drawn into theliquid removal device but the perforated plate will prevent large unevenflows that may cause vibration. Micro-sieves made by electroforming,photoetching and/or laser cutting can be used as the plate 21. Suitablesieves are made by Stork Veco B.V., of Eerbeek, the Netherlands. Otherporous plates or solid blocks of porous material may also be used,provided the pore size is suitable to maintain a meniscus with thepressure differential that will be experienced in use.

FIG. 8 shows a liquid removal device incorporated in a seal member 12 ofand immersion hood IH, according to a particular embodiment of theinvention. FIG. 8 is a cross-sectional view of one side of the sealmember 12, which forms a ring (as used herein, a ring may be circular,rectangular or any other shape) at least partially around the exposurefield of the projection system PL (not shown in FIG. 8). In thisembodiment, the liquid removal device 20 is formed by a ring-shapedchamber 31 near the innermost edge of the underside of the seal member12. The lower surface of the chamber 31 is formed by a porous plate 30,as described above. Ring-shaped chamber 31 is connected to a suitablepump or pumps to remove liquid from the chamber and maintain the desiredunderpressure. In use, the chamber 31 is full of liquid but is shownempty here for clarity.

Outward of the ring-shaped chamber 31 are a gas extraction ring 32 and agas supply ring 33. The gas supply ring 33 has a narrow slit in itslower part and is supplied with gas, e.g, air, artificial air orflushing gas, at a pressure such that the gas escaping out of the slitforms a gas knife 34. The gas forming the gas knife is extracted bysuitable vacuum pumps connected to the gas extraction ring 32 so thatthe resulting gas flow drives any residual liquid inwardly where it canbe removed by the liquid removal device and/or the vacuum pumps, whichshould be able to tolerate vapor of the immersion liquid and/or smallliquid droplets. However, since the majority of the liquid is removed bythe liquid removal device 20, the small amount of liquid removed via thevacuum system does not cause unstable flows which may lead to vibration.

While the chamber 31, gas extraction ring 32, gas supply ring 33 andother rings are described as rings herein, it is not necessary that theysurround the exposure field or be complete. In an embodiment, suchinlet(s) and outlet(s) may simply be circular, rectangular or other typeof elements extending partially along one or more sides of the exposurefield, such as for example, shown in FIGS. 2, 3 and 4.

In the apparatus shown in FIG. 8, most of the gas that forms the gasknife is extracted via gas extraction ring 32, but some gas may flowinto the environment around the immersion hood and potentially disturbthe interferometric position measuring system IF. This can be preventedby the provision of an additional gas extraction ring 35 outside the gasknife, as shown in FIG. 8A.

Because in this embodiment, the liquid removal system can remove most,if not all, of the immersion liquid while at a height of 50 to 300 μmabove the surface of the substrate W or the substrate table WT, lessonerous requirements are put on the seal member vertical position thanwhen a gas bearing is used to confine the immersion liquid. This meansthat the seal member may be positioned vertically with a simpleractuation and control system. It also means that the requirements on theflatness of the substrate table and substrate are reduced, making iteasier to construct devices such as sensors which need to be provided inthe upper surface of the substrate table WT.

Removal of most of the liquid without evaporation also means thattemperature gradients may be reduced, avoiding thermal deformation ofthe substrate, which can lead to printing errors. Evaporation may alsobe further minimized by using humid gas in the gas knife, e.g. with arelative humidity of about 50 to 75%, in combination with a pressuredrop of about 100 to 500 mbar and a flow rate of about 20 to 200 l/min.

Variants of this embodiment of the invention are shown in FIGS. 9 to 11.These variants are the same as that described above except in relationto the shape of the porous plate 30.

As shown in FIG. 9, the porous plate 30 a can be set at a slight angle,so that it is higher at the outside. The increasing gap between theporous plate 30 a and substrate W or substrate table WT with distancefrom the center of the exposure field, changes the shape of the meniscus11 a and helps to ensure that the area that is immersed in liquid has amore or less constant width.

In the variants shown in FIGS. 10 and 11, sharp corners 35 are used tolimit the position of the meniscus 11 a which is held by surface tensionat the sharp corner. The sharp corner can be an obtuse angle, as shownin FIG. 10, or a right angle, as shown in FIG. 11. The shape of the gasextraction ring 32 can be adjusted as necessary.

A seal member according to another particular embodiment of theinvention is shown in FIG. 12, which is a similar view to FIG. 8.

In the embodiment of FIG. 12, a liquid bearing 36 is used to at leastpartially support the seal member 12, in place of separate actuators.The liquid, or hydro-dynamic, bearing 36 is formed by immersion liquidsupplied under pressure to liquid supply chamber 37, in a known manner.The liquid is removed via two-phase extraction chamber 38, which isconnected to suitable pumps (not shown) capable of handling thetwo-phase flow. A gas knife 34 confines the immersion liquid in the samemanner as in previous embodiments.

The use of a liquid bearing 36 enables the seal member 12 to bemaintained at a height of about 50 to 200 μm above the substrate W orsubstrate table WT, easing control and flatness requirements asdescribed above. At the same time, the two-phase extraction reduces thenumber of chambers that need to be formed in the seal member 12 and thenumber of hoses that need to be provided to it.

A porous plate 30 is provided across the bottom of two-phase extractionchamber 38, to control the flow of gas and liquid into it. By suitableselection of the size, number and arrangement of the pores in thisplate, the two-phase flow is made steady, avoiding uneven flow that maycause vibrations. As in the embodiments described above, a micro-sievemay be used as the plate 30.

Also as described in relation to the embodiment above, an inclination ora sharp edge may be provided in the porous plate 30 to control theposition of the meniscus of the immersion liquid 11. Again, the removalof any residual liquid can be effected by a high-humidity, large flowgas knife 34 and the pressure of the gas knife can also be used tocontrol the meniscus position.

In this, and other, embodiments of the invention, the shape of the partof the seal member that is in the immersion liquid may be adjusted toprovide a desired degree of damping of vertical movements of the sealmember 12. In particular, the width L_(da), and hence area, of a part ofthe seal member which confines the liquid 11 into a narrow passage canbe selected to provide the desired damping. The amount of damping willbe determined by the area of the damping region, its height h_(da) abovethe substrate W or substrate table WT, the density ρ of the immersionliquid and its viscosity η. Damping may reduce variations in theposition of the seal member due to vibrations, e.g. caused by unevenfluid flows.

A porous plate 41 may also be used to control the flow in an overflowdrain 40, as shown in FIG. 13. The overflow drain of FIG. 13 may beapplied in any of the embodiments of the invention described herein. Theoverflow drain is provided in an upper surface of the seal member 12 ata relatively large radius from the center of the seal member 12. In casethe space between the final element of the projection system PL and thesubstrate W becomes overfull of immersion liquid, the excess liquid willflow onto the top of the seal member 12 and into the drain 40. The drain40 is normally full of liquid and maintained at a slight underpressure.The porous plate 41 prevents gas being drawn into the overflow drain butallows liquid to be drained away when required. The porous plate mayalso be set at a slight angle to the horizontal.

A porous separator can also be used in a manifold 50 that is provided ina liquid drain system that takes a two-phase flow from the immersionhood IH. As shown in FIG. 14, the two-phase flow 51 is discharged into amanifold chamber 51 in which the liquid and gas separate. The gas isremoved from the top of the manifold by a gas outlet 52 which is kept ata pressure of about −0.1 barg by a suitable vacuum pump and pressurecontroller. A liquid removal pipe 53 extends to near the bottom of themanifold and is closed by a porous plate 54. The liquid removal pipe 53is kept at a pressure below the bubble point of the porous plate 54,e.g. about −0.5 barg, With this arrangement, even if the liquid level inthe manifold drops below the bottom of the pipe 53, no gas will be drawnin to it, preventing any unwanted fluctuation in the pressure of themanifold 50, which might be communicated back to the immersion hood IHand cause a disturbance.

A variation of the manifold is shown in FIG. 15. In this variant, whichis the same as that of FIG. 14 save as described below, the manifold isthermally isolated from its surroundings. The low pressure flow throughthe manifold causes evaporation of the immersion liquid, leading tocooling. If the manifold is positioned close to or in thermal contactwith a temperature sensitive part of the lithographic apparatus, such asa reference or metrology frame supporting, for example, the projectionsystem and/or measurement equipment, such cooling may have anundesirable effect,

The manifold is therefore formed as a double-walled tank, comprisinginner tank 50 a and outer tank 50 b, with a flow of temperaturecontrolled liquid, e.g. water, between the walls of the inner and outertanks. The temperature controlled liquid is supplied at inlet 55 andremoved at outlet 56. A series of baffles 57 are arranged in the spacebetween the walls of the two tanks to ensure there are no regions ofstagnant liquid. To avoid bridging the thermal isolation afforded by thedouble walled tank, no baffle contacts both inner and outer tanks. Therate of flow of temperature controlled liquid is determined to keep thetemperature deviation of the outer tank 50 b within limits imposed byany nearby temperature-sensitive component. In an embodiment, an air gapor additional thermal insulation is also provided between the outer tankand any nearby temperature-sensitive component.

A liquid supply system 60 that may be used in embodiments of theinvention is shown in FIG. 16. It comprises, in series: a source 61 ofimmersion liquid, e.g. a fab supply of ultra pure liquid; a constantflow restrictor 62; a variable flow restrictor 63; and a pressureregulator 64 with an external tap, a variable restriction 65 and aconstant restriction 66, positioned just before the immersion hood H.The pilot line for the pressure regulator 64 is connected downstream ofthe variable restriction 65 and so the input to the constant restriction66 is at a constant pressure, hence the flow into the immersion hood isat constant pressure and rate.

An alternative liquid supply system 60′ is shown in FIG. 17. This systemis the same as the system 60 except as described below. In place of theregulator 64 and fixed restriction 66, a forward pressure regulator 67and backward pressure regulator 68 are provided. Two pressure meters 69a, 69 b are also provided. The forward pressure regulator 67 maintainsthe pressure downstream of it at a predetermined level and the backwardpressure regulator maintains the pressure upstream of it at apredetermined level, in both cases independently of flow rate. Thus thevariable flow restrictor 65 operates with substantially constantupstream arid downstream pressures, avoiding instability. The flow ratecan be adjusted by adjustment of the pressure levels set by the pressureregulators 67, 68 and the variable flow restrictor 65, aided by thepressure sensors 69 a, 69 b which may also be used for monitoringpurposes.

In a lithographic apparatus, a substrate is held on a substrate holder(often referred to as a pimple plate, burl plate or chuck), whichcomprises a flat plate of the same diameter as the substrate having alarge number of small pimples or burls on its major surfaces. Thesubstrate holder is placed in a recess in the substrate table (mirrorblock) and the substrate placed on top of the substrate holder. A vacuumis developed in the spaces between the substrate table and holder andbetween the holder and substrate so that the substrate and holder areclamped in place by atmospheric pressure above the substrate. The recessin the substrate table is necessarily slightly larger than the substrateholder and substrate to accommodate variations in substrate size andplacement. There is therefore a narrow groove or trench around the edgeof the substrate in which immersion liquid may collect. While there theliquid causes no harm but it may be blown out of the groove by a gasbearing or gas knife in the immersion hood. Droplets on the substrate orsubstrate table that result may cause bubbles when the liquid meniscusunder the immersion hood meets them.

The substrate holder is generally made of a material having a lowthermal coefficient of expansivity, such as Zerodur or ULE. Some suchmaterials are porous and in that case the surface pores are filled in toprevent contaminants becoming trapped there. However, it is proposed toleave the surface pores unfilled around the edge of the substrate holderand/or in a peripheral region. Then, when the substrate holder is usedin an immersion lithography apparatus, the immersion liquid entering thegroove will enter the pores of the substrate holder and not be blown outby the gas bearing or gas knife. If the substrate holder has anopen-celled structure, the immersion liquid that has entered its porescan be removed by the vacuum system that clamps the substrate and holderto the table.

As shown in FIG. 18, an extraction channel 70 connected to a volume 11from which only liquid is to be extracted via a narrow capillary 71 withhydrophilic walls 72 may be arranged so that liquid, e.g. water, isextracted by suitable underpressure −p, but when no liquid is present inthe volume 11 a meniscus 73 prevents entry of gas, e.g. air. Conversely,as shown in FIG. 19, an extraction channel 80 connected to the volume 11via a capillary 81 with hydrophobic walls 82 extracts gas, e.g. air, butwhen liquid, e.g, water, is present meniscus 83 prevents further flow.The exact level of underpressure −p for these arrangements will dependon the liquid and gas involved, the size of the capillary and thecontact angle of the liquid to the walls of the capillary, However, fora capillary of about 0.05 mm width, an underpressure of about 20 mbarmay be suitable to enable selective extraction of water or air.

Extraction arrangements of this type can be used to selectively removeliquid or gas form any desired part of the lithographic apparatus. Anadvantageous use is shown in FIGS. 20a to 20d , where liquid extractionchannel 70 and gas extraction channel 80 are both connected to a trenchin the substrate table WT around the edge of the substrate W. When thesubstrate edge is under the projection system and hence the trench isfilled with liquid, channel 70 extracts liquid so that there is a flowof liquid downwards. This draws any bubbles that might form in thetrench, e.g. due to incomplete filling, downwards and to a positionwhere the gas may be extracted via channel 80, but they will not enterthe channel 70. When the substrate edge is no longer under theprojection system, the trench can quickly be emptied. In this way,escape of bubbles to interfere with imaging is reduced or prevented. Byseparating the liquid and gas flows, instabilities which may causevibrations may be avoided and the cooling effect of evaporation may bereduced or minimized.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substrateusing a projection system and having a liquid supply system arranged tosupply a liquid to a space between the projection system and thesubstrate, comprising a fluid removal system including a chamberconfigured to hold liquid and having an open end adjacent a volume inwhich fluid will be present, the open end configured to remove, througha pressure differential across the open end when liquid is present inthe chamber, substantially only liquid from the volume when liquid inthe volume is adjacent the open end but not gas from the volume when gasin the volume is adjacent the open end.

In an embodiment, the fluid removal system is arranged to remove liquidfrom a volume adjacent the space. In an embodiment, the apparatusfurther comprises a member at least partially surrounding the space andcomprising the open end in a surface of the member facing the substrate.In an embodiment, the member further comprises a gas supply devicehaving an outlet in a surface of the member facing the substrate so asto form a gas knife to remove residual liquid from a surface of thesubstrate, the gas knife being located radially outwardly of the openend. In an embodiment, the open end comprises a porous member comprisinga plurality of apertures. In an embodiment, the open end comprises acapillary conduit having a hydrophilic wall. In an embodiment, thecapillary conduit has a width of about 0.05 mm and the fluid removalsystem is configured to provide an underpressure of about −20 mbar tocreate the pressure differential, when the liquid is water and the gasis air. In an embodiment, the fluid removal system comprises aliquid/gas separation manifold thermally isolated from its surroundingsand the chamber comprises a pipe extending into a lower part of themanifold. In an embodiment, the liquid supply system comprises, inseries before outlet to the space, a pressure regulator with an externaltap, a variable restriction, and a constant restriction, the externaltap connected downstream of the variable restriction and configured sothat an input of the constant restriction is at a substantially constantpressure. In an embodiment, the liquid supply system comprises, inseries before outlet to the space, a forward pressure regulator with anexternal tap connected downstream of it, a variable restriction, and asecond pressure regulator with an external tap connected upstream of it,the external tap of the forward pressure regulator connected upstream ofan input of the variable restriction and the external tap of thebackward pressure regulator connected downstream of an output of thevariable restriction, the forward and backward pressure regulatorsconfigured to maintain substantially constant pressures at the inlet andoutlet of the variable restriction.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substrateusing a projection system and having a liquid supply system arranged tosupply a liquid to a space between the projection system and thesubstrate, comprising a fluid removal system including a chamberconfigured to hold gas and having an open end adjacent a volume in whichfluid will be present, the open end configured to remove, through apressure differential across the open end when gas is present in thechamber, substantially only gas from the volume when gas in the volumeis adjacent the open end but not liquid from the volume when liquid inthe volume is adjacent the open end. In an embodiment, the open endcomprises a capillary conduit having a hydrophobic wall. In anembodiment, the open end comprises a porous member comprising aplurality of apertures. In an embodiment, the chamber configured to holdgas is a first chamber and its open end is a first open end and furthercomprising a second chamber configured to hold liquid and having asecond open end adjacent the volume, the second open end configured toremove, through a pressure differential across the second open end whenliquid is present in the second chamber, substantially only liquid fromthe volume when liquid in the volume is adjacent the second open end butnot gas from the volume when gas in the volume is adjacent the secondopen end. In an embodiment, the apparatus further comprises a substratetable configured to hold the substrate and comprising the first open endand the second open end in a surface of the substrate table adjacent anedge of the substrate, when the substrate is held on the substratetable. In an embodiment, the first open end comprises a capillaryconduit having a hydrophobic wall and the second open end comprises acapillary conduit having a hydrophilic wall.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substrateusing a projection system and having a liquid supply system arranged tosupply a liquid to a space between the projection system and thesubstrate, comprising a fluid removal system including a capillaryconduit having an open end adjacent a volume in which fluid will bepresent, the capillary conduit configured to remove, through a pressuredifferential across the capillary conduit substantially only liquid fromthe volume or to remove, through a pressure differential across thecapillary conduit, substantially only gas from the volume.

In an embodiment, the fluid removal system is arranged to remove liquidfrom a volume adjacent the space. In an embodiment, the apparatusfurther comprises a member at least partially surrounding the space andcomprising the capillary conduit with the open end in a surface of themember facing the substrate. In an embodiment, the apparatus furthercomprises a substrate table configured to hold the substrate andcomprising the open end in a surface of the substrate table adjacent anedge of the substrate, when the substrate is held on the substratetable. In an embodiment, the capillary conduit has a width of about 0.05mm and the fluid removal system is configured to provide anunderpressure of about −20 mbar to create the pressure differential,when the liquid is water and the gas is air. In an embodiment, thecapillary conduit has a hydrophobic wall when configured to removesubstantially only gas or a hydrophilic wall when configured to removesubstantially only liquid.

In European Patent Application No. 03257072.3, the idea of a twin ordual stage immersion lithography apparatus is disclosed. Such anapparatus is provided with two tables for supporting a substrate.Leveling measurements are carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus has only one table.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively, The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, where applicable, the invention may takethe form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein.

The present invention can be applied to any immersion lithographyapparatus, in particular, but not exclusively, those types mentionedabove. The immersion liquid used in the apparatus may have differentcompositions, according to the desired properties and the wavelength ofexposure radiation used. For an exposure wavelength of 193 nm, ultrapure water or water-based compositions may be used arid for this reasonthe immersion liquid is sometimes referred to as water and water-relatedterms such as hydrophilic, hydrophobic, humidity, etc. may be used.However, it is to be understood that embodiments of the presentinvention may be used with other types of liquid in which case suchwater-related terms should be considered replaced by equivalent termsrelating to the immersion liquid used.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

The invention claimed is:
 1. A substrate support for an immersionlithographic apparatus configured to project a radiation beam, using aprojection system, onto a substrate via liquid supplied to a spacebetween the projection system and the substrate, the substrate supportcomprising: a body configured to support the substrate and configured tobe removably supported on a movable substrate stage structure in theimmersion lithographic apparatus; and an extractor arrangement locatedat least partly in the body, the extractor arrangement configured toremove fluid and extraction piping of the extractor arrangement having ahydrophobic wall inside the body.
 2. The substrate support of claim 1,wherein a trench is formed adjacent an edge of the substrate when thesubstrate is supported by the substrate support, and the extractionpiping is in fluid communication with the trench.
 3. The substratesupport of claim 1, wherein the extraction piping is configured suchthat fluid is extracted by suitable under-pressure.
 4. A substratesupport for an immersion lithographic apparatus configured to project apatterned beam, using a projection system, onto a substrate via liquidsupplied to a space between the projection system and the substrate, thesubstrate support comprising: a body configured to support the substrateon a support plane defined by a plurality of projections, the bodyconfigured to be removably supported on a movable substrate stagestructure in the immersion lithographic apparatus; and an extractorarrangement located at least partly in the body with at least part ofextraction piping of the extractor arrangement located at or below thesupport plane, the extractor arrangement having an opening in or on thebody, the opening sized so as to remove fluid and at least part of theextractor piping having a hydrophobic wall inside the body.
 5. Thesubstrate support of claim 4, wherein the extraction piping isconfigured such that fluid is extracted by suitable under-pressure. 6.The substrate support of claim 4, wherein the body has a hydrophilicwail.
 7. The substrate support of claim 4, wherein the opening and theextraction piping are configured to remove, through a pressuredifferential across the opening and/or the extraction piping,substantially only liquid into the extraction piping.
 8. The substratesupport of claim 4, wherein the extractor arrangement is configured toextract liquid using an underpressure and further, in the absence ofliquid adjacent the opening, a meniscus substantially prevents entry ofgas into the extraction piping.
 9. The substrate support of claim 1,wherein the body has a hydrophilic wall.
 10. The substrate support ofclaim 1, wherein an opening of the extraction piping and the extractionpiping are configured to remove, through a pressure differential acrossthe opening and/or the extraction piping, substantially only liquid intothe extraction piping.
 11. The substrate support of claim 1, wherein theextractor arrangement is configured to extract liquid using anunderpressure and further, in the absence of liquid adjacent an entranceof the extraction piping, a meniscus substantially prevents entry of gasinto the extraction piping.
 12. A substrate support for an immersionlithographic apparatus configured to project a patterned beam, using aprojection system, onto a substrate via liquid supplied to a spacebetween the projection system and the substrate, the substrate supportcomprising: a body configured to support the substrate and configured tobe removably supported on a movable substrate stage structure in theimmersion lithographic apparatus; and extraction piping located at leastpartly in the body, at least part of the extraction piping in or on thebody is in fluid communication with the space and configured to removeliquid via a capillary action.
 13. The substrate support of claim 12,wherein the extraction piping is configured such that the liquid isextracted by suitable under-pressure.
 14. The substrate support of claim12, wherein a trench is formed adjacent an edge of the substrate whenthe substrate is supported by the substrate support, and the extractionpiping is in fluid communication with the trench.
 15. The substratesupport of claim 12, wherein a portion of the body below a top surfaceof the body comprises a hydrophobic surface.
 16. The substrate supportof claim 12, wherein a portion of the body below a top of the bodycomprises a hydrophilic surface.
 17. The substrate support of claim 12,wherein the extraction piping is configured to extract the liquid usingan underpressure and further, in the absence of liquid adjacent anentrance of the extraction piping, a meniscus substantially preventsentry of gas into the extraction piping.
 18. The substrate support ofclaim 12, wherein the body comprises a plurality of projectionsprotruding from a surface of the body.
 19. The substrate support ofclaim 1, wherein the extraction piping comprises a conduit with anopening in a surface of the body and a channel with a largercross--section than the conduit, the conduit opening into the channel.20. The substrate support of claim 4, wherein the extraction pipingcomprises a conduit having the opening in a surface of the body and achannel with a larger cross-section than the conduit, the conduitopening into the channel.